The instant invention pertains to the conversion of an oil feedstock to hydrocarbon products. In one aspect, the invention relates to catalytic cracking wherein a feedstock stream and catalyst are contacted in a reactor.
It is known that atomization of an oil feedstock stream for mixing with catalyst enhances many reactions. This is so because increased atomization increases the surface area of the oil and thereby increases heat transfer to the oil. Such heat transfer first vaporizes and thereafter drives the catalytic reactions.
Atomization of the oil as it enters the riser reactor in a fluid catalytic cracking unit is particularly important when converting heavy oils which have an initial boiling point generally in the temperature range of 600.degree.F. to 1200.degree.F. Heavy oils are especially difficult to crack to valuable products because their high boiling point and viscosity make satisfactory vaporization very difficult.
Heavy oils can be successfully cracked into desirable products where they have been vaporized prior to contact with the catalyst. With conventional feeds, vaporization is achieved by radiant energy transfer from the hot cracking catalyst to the feed droplets. This type of vaporization mechanism is satisfactory for oils that are vaporized below thermal cracking temperatures which commence at about 850.degree.F. For heavy oils, however, vaporization may not be completed prior to the onset of thermal cracking and coke formation. Further, coke laydown is worsened where liquid oil strikes the hot catalyst particles. An apparatus and process for vaporizing a heavy oil would clearly be desirable.
It is common to pre-heat an oil feedstock in order to enhance vaporization and cracking of the oil in a fluid catalytic cracking unit. When the feedstock is so heated, some of the oil is vaporized prior to its introduction to a nozzle for atomization. Thus, the feedstock stream may comprise a two phase flow consisting of steam and oil vapor, on one hand, and liquid oil when it is injected into the nozzle for atomization. Atomization of two phase fluids increases nozzle wear. Also, nozzle atomization of a two phase fluid results in less efficient atomization than when a single liquid phase is introduced to the nozzle. Further, slugs of liquid and gas emitted from the nozzle can momentarily disrupt the catalyst-oil ratio in the unit, changing product distribution. It would be clearly desirable to provide an apparatus and process in which the liquid phase of a two phase hydrocarbon feedstock stream may be fully atomized when it is introduced to the riser reactor of a fluid catalytic cracking unit or otherwise contacts oil vapor from the preheating of the feedstock.
It is an object of the present invention to provide a process for atomizing an oil feed for catalytic conversion.
It is another object of the invention to provide such a process in which the liquid oil in a two phase feedstock stream is atomized into vapor and tiny droplets when introduced into a reactor for catalytic conversion.
It is another specific object of the invention to provide such a process in which wear on the oil nozzle used to introduce liquid oil into a reactor for catalytic conversion is substantially reduced.
It is still another object of the present invention to provide such a process which permits use of a shorter riser reactor and/or increases cracking yields and/or a reduces the severity of catalytic cracking unit operating conditions.
In one aspect, the invention comprises a process for catalytic conversion of hydrocarbons in which an oil feedstock is separated into vapor and liquid components. Thereafter, each of the separated components is separately introduced into a reactor for catalytic conversion. The process may include the steps of heating the feedstock prior to separation into vapor and liquid components and mixing the feedstock with steam prior to heating of the feedstock. In another aspect of the invention, the liquid component is atomized prior to introducing the same into a reactor for catalytic conversion. The atomization may be achieved by providing a liquid component under pressure to the throat of a venturi atomizer.
In yet another aspect of the invention, apparatus is provided for performing the process.